The invention relates to a method for producing enzyme granulates, enzyme granules thus produced, and their use for producing formulations containing said enzyme granulates, (with their use simultaneously being part of a potentially preferred variant of the production method for the enzyme granulates), a method for producing enzyme granulates and/or the use of enzyme granulates thus produced, as well as further preferred embodiments of the invention shown in the following description and the subsequent claims.
Enzymes are used in a multitude of industrial fields in an ever increasing extent. This relates both to the amounts produced as well as the variety of forms of enzymes. Generally, enzymes are present in a liquid form or as a dry substance. Most recently, granulates have been used more and more as a preferred trade good by the users or by the processing industry. The granulates are characterized in advantageous features, such as easy dosing, very good flow characteristics, homogenous internal structures, high particle density, low dust content, as well as an even and well-closed surface. Due to the fact that enzymes can generally be characterized by their particular features, such as instability in an aqueous environment and their allergenic reactions, for example, the form of granulates has proven an advantageous trading form.
The stability of enzymes can be improved by converting them into a dry form. This can occur, for example, by spray drying, various agglomeration processes (wet granulation in mixers and/or fluidized bed devices (spray granulation).
Spray drying has the disadvantage that the devices require very large volumes and the powdery product contains a considerable content of dust.
In order to reduce this dust content, spray drying is frequently performed via a multi-stage drying device. It is disadvantageous that enzyme granulates produced in such multi-stage drying devices are provided with a poor, i.e. high rounding factor (lists the ratio of the surface of a granule in reference to the surface of a perfectly round granule) exceeding 1.6. Due to the low roundness and thus easily separating protruding sections, enzyme granulates with a rounding factor exceeding 1.6 quickly lead to a high dust content under mechanical stress occurring for example during packaging and transportation.
This dust content requires particular protective measures for the production personnel and the users as well as considerably higher expenses in plant engineering for the removal of dust, ventilation, and recycling of dust.
One potential method for producing enzyme granulates is presented in the buildup granulation in fluidized beds as published in WO 01/83727 A2. Here, a method is shown, in which the liquid enzyme formulation is injected via a nozzle into a fluidized bed. The dust developing in the process is separated from the exhaust and is recycled as seeds for the granulation process. The developing granulates are removed from the process using one or several gravity sifters arranged in the injection floor of the fluidized beds. The size of the granulates removed can be adjusted by controlling the gas amount in the sifter. Optionally, the granulates can additionally be coated. The process uses the fluidized bed process according to EP-A-0163836 and EP-A-0332929.
The described fluidized air process is characterized in an injection floor being provided over the entire cross-section of the fluidized bed for the homogenous distribution of the processing gas required for the fluidization and drying. The nozzles used for injecting the liquid spray vertically upwards and are directly integrated into the injection floor (EP-A-0332929) or surrounded by a sifter at the height of the injection floor (EP-A-0163836). The granulation seeds necessary for the process are produced by partial spray drying of the injected liquid by a partial non-covering (through spray) of the nozzles with the material in the fluidized bed. The mass of the fluidized bed is formed by a balance between the spray-dried seeds and by the recycled seed from sifting as well as the granulates discharged. A separation of granulates that are too large does not occur.
Caused by the introduction of the liquid, the particles contained in the fluidized bed are moistened in the injection area and drying of the moisture film on the surface of the particles occurs. Outside of the nozzles, in the remaining area of the fluidized bed essentially no drying of superficially moistened particles occurs. Instead, only a small portion of the moisture contained in the pores of the particles evaporates, which leads to an increase in the (core) particle temperature. However, in conventional fluidized beds an introduction of heated processing gas is necessary outside the spray area of the nozzles, as well, in order to mix the particles inside the device and to continuously move the particles in the injection zone. Due to the fact that the production of enzymes is temperature sensitive, these known processes cannot achieve an optimum yield in activity of enzymes (low relative activity in reference to the originally used enzyme activity, i.e., in addition to active enzymes, a large portion of deactivated or destroyed enzyme is present, which means that more enzyme must be used for the same amount of overall activity [absolute activity]). Additionally, uneven temperature distribution cannot be avoided in the production process.
In the process progression, the dwell time can be avoided in the systems described only in that the drying of the granulates does not occur up to the required final value and/or enzyme granulates of a smaller grain size are produced, which however influence the quality of the enzyme granulates. The enzyme granulates produced according to prior art have a high content of inactive carrier material and, thus a low absolute activity, a high content in deactivated enzyme (low relative activity), a low value of average grain size D50 (grain size, in which 50% by weight of the particles have a diameter smaller and 50% by weight of the particles a diameter greater than the average grain size D50), or a high moisture content, or usually two or three of these features.
For example, according to a method described in WO 01/83727 A2 a yield of enzyme activity higher than 85% can be achieved (in reference to the theoretically possible overall enzyme activity) having only small particles and/or a moisture content (residual moisture) of more than 5%.
On the other hand, WO 98/55599 describes a method for producing enzyme granulates using an extruder and a rounding device for use with a carrier material (such as corn starch). This method has also been described in example 2 of WO 01/83727.
Here, a yield of enzyme activity reaching 95% is achieved (relative enzyme activity) and a granulate having average grain sizes D50 of 600 μm, a moisture content of 5%, and a roundness factor of 1.4. This method is disadvantageous in that an enzyme preparation with 27% starch in the dry substance must be added to the mixture at a weight ratio of 1:2, in order to achieve a mixture that can be extruded. This way, the enzyme granulates yielded by this extrusion method is provided with a content of active enzyme material being less than 13% (absolute enzyme activity) in reference to the dry substance.
The enzyme granulates that can be yielded with the spray drying process according to WO 01/83727 results in granulates with a roundness factor in the preferred range from 1 through 1.6, though, and also with particles having an average grain size D50 of 620 μm (cf. table 2, experiment 2), however the content of inactive carrier material is much lower, resulting in the content of overall enzyme (active and deactivated) being higher than in the product of the process described in WO 98/55599. However, in the enzyme granulates according to WO 98/55599 it is disadvantageous that the relative portion of active enzyme, in reference to the overall amount of active and deactivated enzyme, is considerably lower, being 85%, than in the extrusion process, which is also discernible from example 2 mentioned in WO 01/83727.
According to the working mode described in WO 01/83727 the enzyme granulates are produced according to the method of to EP 0 332 929. This method is characterized in that the content of the bed adjusts itself (see EP 0 332 929, page 22, line 27). This way, the residence time cannot be controlled for a certain granulation performance. In example 1 the content of the fluidized bed amounts to 3 kg and the granulation yield is 1.5 kg/hour with the granulation occurring from an aqueous saline solution with a content of 23% by weight of dry matter. The residence time is also fixed to 2 hours in this case. Therefore, the residence time is here determined by the ratio of the content of the bed in reference to the granulation yield in kg/hour.